Planetary Radio: Space Exploration, Astronomy and Science - The News From Saturn-With Linda Spilker

Episode Date: June 26, 2019

It has been many months since the great Cassini spacecraft plunged into Saturn’s atmosphere and fiery death.  Yet the mission lives on as the reams of data and images reveal much more of this beautiful world, its rings and its moons.  Project Scientist Linda Spilker is back with Mat to provide a fascinating update. We close with Bruce Betts and and a What’s Up segment that anticipates the mission of LightSail 2. Learn more about all of this week’s topics at:  http://www.planetary.org/multimedia/planetary-radio/show/2019/0626-2019-cassini-update-spilker.htmlLearn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

The latest news from Saturn with Linda Spilker, this week on Planetary Radio. Welcome. I'm Matt Kaplan of the Planetary Society, with more of the human adventure across our solar system and beyond. A slightly abbreviated show this week as I prepare to leave for Florida in a few hours. I'll be joined by many of my colleagues, hundreds of Planetary Society members, and thousands of other space fans headed to the Cape for the launch of the third SpaceX Falcon Heavy. Among the 24 payloads carried by that big rocket is the Planetary Society's LightSail 2.

Actually, by the time you hear this, we hope LightSail 2 will be safely in orbit. With a successful static test on the evening of June 19th, launch is set for the late evening of Monday, June 24th. But you know how launches are. Anyway, I've got a great way to distract you and myself from our attempt to orbit a solar-sailing CubeSat. Linda Spilker is still my most frequent guest on Planetary Radio. She is the project scientist for the Cassini-Huygens mission that ended on an early September morning in 2017. Or did it? You almost wouldn't know,

judging from the amount of science that is still flowing from the mission's data. And much of that science is spectacular. Linda, as always, a pleasure to welcome you back to Planetary Radio, especially here in the Planetary Society studio. Happy 15th anniversary of reaching Saturn with Cassini. Oh, well, thank you very much, Matt. It's a pleasure to be here. I surprised you with that one.

Yes, you did. Because I looked it up, and I was surprised to see that it's that nice anniversary. And we can celebrate by talking about the great science that continues to flow from this mission, which has been vaporized in the Saturnian atmosphere for a year and a half now. That's right. That's right. And yet the analysis of the data continue. There's so much we're still finding. It's this treasure trove of data sent back by Cassini. And we've learned so much more about the rings, the planet, the icy moons, and lots more to come. We last talked in October. It was right after another of these big releases of data in papers that were published in Science Magazine. There must be other journals that are

very envious. That could be, Matt. That could be. So we talked about all the stuff there. And now you've got new science. It's kind of a shame we haven't talked sooner than this because so much has been going on. And the big one that I think captured more popular media attention, not just, you know, folks like us who are science and space geeks, was that January 17 publication in Science, the one that really made a splash because it told everybody that the rings are, what, relatively youthful. That's right, Matt. The rings are much younger than the 4.5 billion year age of the solar system. In fact, there may be only 10 to 100 million years old. Maybe the rings formed around the age of the dinosaurs. Imagine dinosaurs looking up and all of a sudden, wow, look, that planet has rings.

Well, I was thinking that, you know, humanity, we're kind of lucky that we've reached this stage where we have telescopes and there they are. I mean, we could have missed lucky that we've reached this stage where we have telescopes and there they are. I mean, we could have missed this if we'd been off by 10 million years in our evolution. That's absolutely right. In fact, the rings are slowly decaying. Particles are getting lost to Saturn, to space, and in maybe another few hundred million years, they might be gone. How critical to that discovery was getting in close to Saturn? Well, the only way, Matt, we could do that was to dive through the gap between the planet and the rings and make very sensitive gravity measurements of Saturn. And

then Saturn on one side, the rings on the other, feeling those minute tiny tugs. And from that, we could actually then figure out the mass, how much material would be in the rings if you scooped them all up and formed them into a moon. So do we now know not only what the rings weigh, what their mass is really, but the mass of Saturn itself? Right, we know the mass of Saturn very accurately as well as the rings. And what's surprising is the rings were only about 50% as massive

as we expected. A lot of the scientists, we even had a little pool, how massive would the rings be? And a lot of people were saying more massive than the estimates made by Voyager. And so they just turned out to be much less massive, pointing to a younger age. How were we far off? How was it that so many people were thinking that if we were wrong, we were wrong in the other direction, that they were more massive than we thought? Well, the puzzle came with the most massive ring at Saturn, the B-ring. And we got estimates of the mass from looking at how waves dampen the rings, but the B ring was so thick, it blocked all the starlight, it blocked radio waves. So we couldn't directly estimate its mass. So we just said, okay,

it looks like it's so thick, it must be very massive. And that's where our estimates came from. But it turns out there must be something else going on because that ring is not nearly as massive as we expected. So somehow the particles are interacting with each other to block starlight, block radio waves, and yet not be quite as massive. A good example is if you think about a swimming pool full of water. You can look through that water, see the bottom of the swimming pool, and yet that water has a lot of mass. Now imagine a very thick fog.

That very thick fog will keep you from seeing, say, to the next house or down the street, and yet there's far less water in that fog. It's just because of how those tiny little droplets of water are reflecting or absorbing the light. So maybe some kind of an analogy like that's going on in the B-ring. It's not, you know, the more massive like the water in the pool, but instead somehow more like a fog. Obviously, the science keeps building on itself. You keep adding to what we've learned. If we move on to March, again in Science Magazine, March 28, all these new findings about these five tiny moons that are in and near the rings,

again, we now know so much more because you were able to take a chance at the end of the mission and fly in there close. This has been full of surprises too, I think. You found that Enceladus has some influence there too. Absolutely, Matt. It turns out that before we hopped across the rings and flew through the gap, we brought the orbit in very close to the outer edge of the F-ring. brought the orbit in very close to the outer edge of the F ring. And by getting in close, we could time it then to get our best ever images of some of these tiny ring moons.

Two of them are in gaps. Pan is in the Encke gap, Daphnis in the Keeler gap, Atlas just outside the outer edge of the A ring, and then Pandora, a couple of the other moons as well. And we found, much to our surprise, that these little tiny moons looked like worlds that there was a central shard or central object, but then it had these big skirts of ring particles around the moon. The rings are only on average maybe 10 feet thick, and so these ring particles accumulate around the equators,

giving them kind of look sort of like a ravioli or maybe a ballerina in a skirt or something. I saw that term used. I know it was a quote from your colleague, Bonnie Barati, who led a lot of this work that led to this publication in March. So like a big belt around the middle of these little moons. That's right. Made completely of ring particles.

And that belt or that skirt can only grow so large until it gets to the point where Saturn's gravity is just balanced by the moon's gravity. And so a particle just won't stick any longer. So the skirts grow to a certain characteristic size. We found that the skirts and the moons themselves have a lot of porous, a lot of empty space. You know, maybe half of it is empty. And then their colors, depending on where they're located, if you're in the rings, then of course you're reddish and your colors look a lot like the ring particles. But as you move away from the rings, those tiny particles from the E ring and from Enceladus

play more and more of a role, and so those moons start to get bluer, especially on the side that sweeps up the particles from Enceladus. So we're seeing this really fascinating interplay between the rings and the moons and also with the E ring and the particles coming in from Enceladus. I'm glad you mentioned that variation in color because there is an illustration, and we'll link to the press releases, the media releases from JPL about all of this stuff. And there is one where it zooms in on one section of the rings, and there are these beautiful, somewhat enhanced, there's a little bit of false color stuff going on here, right? Yes. You're looking across the rings, and it's its own sort of rainbow. It's very amazing.

It's the Keeler gap, and you see tiny Daphnous orbiting in the gap, and it's pulled a small tendril of ring particles away from it, and the rings are very reddish as you move towards Saturn. And yet outside of the Keeler gap, they become grayer and grayer, looking like a very different ring. And so we're puzzled about what's causing that change, that abrupt change right at the gap in color. And then Daphnis is so fascinating. Its orbit is inclined just a little bit relative to the ring plane, and it creates tremendous waves on either edge of the gap.

And the waves not only move in and out relative to Saturn, but up and down as well. So imagine surfing on this giant Daphnis wave of ring particles lifted above and below the ring plane. I was going to bring it up in a couple of minutes, but because you're talking about Daphnis, I mean, there is this image not in the March release, but in the June one, and we'll be coming to that. It's this breathtaking image of Daphnis, this little not quite rock, that is shaping the ring's edge like a world-class sculptor, and it is just so beautiful. Yeah, it's absolutely stunning. You can see three wavelengths of that wave and the final one, the most distant from Daphnis. You can actually see the waves separating from the rings as it gets lifted above and below and then very slowly damps out like waves on a beach until Daphnis comes around again and the process starts over. It's over.

Instead of just a link, I mean, we'll do the link as well, but we'll probably put that image on this week's show page. The people will find it at planetary.org slash radio. But I was looking at it again on my train coming here this morning, and there was this little wisp around Daphnis. And I thought, is that a smudge on my iPad screen? And so I moved it back and forth, and I thought, no, that's part of the image. What was I looking at there? It was this tiny wisp, almost like a tiny little section of a ring around Daphnis itself. Right. Daphnis's gravity had pulled some ring particles away and it made this little curved piece of a ring right next to Daphnis. Just beautiful. Probably some of them are falling onto Daphnis and made some of the skirt that's on Daphnis. Just beautiful. Probably some of them are falling onto Daphnis and made

some of the skirt that's on Daphnis as well. Back to the color. You talked about it being reddest on the inside edges of the rings. Why red? Is that iron oxide or something? What are we looking at there? That composition that causes the redness is really a good question. We know that the rings are mostly water ice. We've seen silicates now in the ring by diving through the gap, and also some complex organics that were measured. So it could also be tiny grains of iron giving it its reddish color. So we're just not completely sure. We know what we saw in the gap, but that's that same material then much, much further away from Saturn. And so we're still puzzling because the spectrometers, the instruments that measure and look at the composition, didn't see organics in

the rings. And if there's a lot of organics there, we should have been able to see it. None of those, and this is the term that has come up several times in recent months on the show, the folins, those complex organics that seem to be down on Titan. Yes. But you just didn't, the instruments didn't see these. Right. The spectrometers, the instruments that measure from a far away remote sensing didn't see them. The instruments that measure from a far away remote sensing didn't see them. But the instruments that flew through the gap and measured in situ, one of those instruments did see organics in the grains and the gases that it measured. We can talk about this at any point in this conversation.

But what you seem to be indicating already is that as much as Cassini has told us, you must be dreaming of yet another mission. Oh, absolutely. As with any mission that reveals all of this very interesting data, there are so many open questions that invariably you say, I want to go back. You know, a mission to fly through the Enceladus plume and look for those big molecules that could indicate life or even land on the surface and send something down into one of those vents. A mission to Titan. There's a proposal in New Frontiers for something called Dragonfly. We've talked about it several times. Quadcopter on Titan would be so cool. And to learn more about what's going on in those methane lakes and seas. And

could you have a very, very unusual kind of life that could live in liquid methane at very, very cold temperatures? Then of course, there's the rings. We actually came up with an orbit after Cassini where you could literally skim across the rings. Titan's orbit is slightly inclined, orbit in the same plane as Titan. And you could then get very, very close across the rings. Titan's orbit is slightly inclined, orbit in the same plane as Titan, and you could then get very, very close to the rings. In fact, I think a great dream would be maybe to have a spacecraft that could hover above with like ion propulsion or something, hover above a patch of ring and watch individual ring particles interact

and look around a propeller and how do propellers grow and why are some places in the rings clumpy and some places streaky and some places kind of look like straw. Really understand that disk of particles, there's lots of analogies for the disk of particles at Saturn in how our solar system might have formed, how mass comes together to form planetesimals for our own solar system and for exoplanet systems as well. So lots of clues there. We just have to

be really good detectives and go back. So I think you know that I'm something of a Trekkie. And I had mentioned to you before we started recording today that I asked you, do you remember or had you seen the opening title sequence for the old Star Trek Voyager? And there is a scene in that when Voyager is making its way across the galaxy, and they are skimming right above the ring system of some planet, so close that you can see the reflection of the spacecraft in the ring itself, on the ring particles. I don't suppose you're talking about getting that close. Right. No, not quite that close, although it'd be tempting to just see how close could you get because the rings in general are only about 10 feet thick, except when you have waves

like the edge of, you know, that Daphnis creates or some of these bending waves, but mostly they're pretty thin. It'd be really cool to see ring particles up close, you know, really get a great portrait of what's going on in the rings and kind of get into their DNA a little bit, if you will. 10 feet, 3 meters, it's one of the most amazing. Every time I hear that, that that's roughly how thick the rings generally are, it is maybe one of the most amazing things that I hear about the Saturnian system. Obviously adds to our fascination.

Right, yeah. Just sort of an average thickness and places that could be much more. Of course, propellers could be half kilometer or kilometer in size. These biggest particles in the rings that are trying to open tiny gaps. And with these final pictures in the final paper, we got some very good, very close pictures and more data on propellers and how they work and what they look like up close. Now, are you talking now about this recent publication? Right, in the June issue. June 13 in the Journal of Science, once again,

more amazing stuff. I already mentioned that image of Daphnis, which really, folks, you have to take a look at. There is another one, though, and it's a slider, so you can interact with it. And it has an image of the rings that was previously published, right? But if you slide it to the left, you see this fantastically complex image. Tell us about that. Right. When you slide it, you're seeing a processed image where it's in particular looking for any structure as muthally as you go around the ring. And by doing some special processing techniques, can start to see these belts of streaky material

or clumpy material or straw-like material. Belts where there's a lot of clumping, you're maybe growing larger and larger strands of ring particles or bigger ring particles, and the bands end abruptly on either side, and then you go to a place where it doesn't look like there's much clumping at all, and then you'll jump to something else. And there's no clear, obvious connection between boundaries. Why do you have these boundaries of clumpiness? And why is it in some places in the rings and yet not in others? And so we just have now a long list of new

questions. How does this work? Why is this clumpiness going on? And we're starting to think it's probably a difference with the surfaces of the particles, that maybe how they collide and interact, maybe somehow the roughness, those grains, regolith grains on the outside of the particles, perhaps could have some influence on how they stick together and how the clumpiness works. But we just have a lot of ideas and still trying to come up with a good model for how this works. and still trying to come up with a good model for how this works. Is there enough data that some people out there are maybe building mathematical models that would help to explain this?

Oh, absolutely, Matt. As we got more data about propellers, about the clumpiness, the modelers are happily going back to work and trying to incorporate this new information into their models. I also read that there was information revealed about impacts and that we may be understanding better what it is that periodically stirs things up, impacts on the rings themselves. Right. Well, how those impacts might generate a lot of dust in a certain region. We think maybe in the D ring, one of the ringlets brightened, perhaps that's evidence of an impact. And maybe as we were flying through the gap, some of those particles is what we saw that got close to Saturn. Saturn's atmosphere slowed them down. And then they finally went into the atmosphere, these

tiniest smoke-sized particles that were filling the gap as Cassini dove through 22 times. Those smoke-like particles, nanoparticles, so tiny, that caused so much anxiety before Cassini went through the gap for the first time. And it turns out you had nothing to worry about. Absolutely. We didn't know. In fact, the first orbit we used the high-gain antenna, that big dish antenna as a shield, to take the particle impacts in case there were millimeter or bigger particles in there. And then we found that we really didn't see much of anything until finally the particle detector said, hey, they're really tiny, like nanograin size. And we said, ah, we can fly through smoke-sized grains. And then we went on

to do all of the science we needed to do. We no longer had to worry about pointing the high-gain antenna into the direction of those particles. Which meant that you couldn't use some of the instruments, right, as you went through the gap because the dish was blocking them? That's right. That's right. In particular for getting samples of those particles, you'd really want to turn the spacecraft 90 degrees and point those instruments into the incoming ring particles. Back to those impacts. What is the thinking now about where that material is coming from?

Is it coming from outside of Saturn or is it stuff that was already there? The nanograins we saw, they're all in the same plane as the ring. So they're coming from the ring. Something has ground up the ring particles, maybe removed a lot of the water and just left the silicates and other materials. There's still water there as well, but it allowed us to see the organics and other material. And then as that boundary, as the atmosphere of Saturn is thick enough, it just slows them down and then they fall into Saturn. Some of the other tiniest grains in the A and B and C rings, they get charged up by Saturn's magnetic field. They can spiral along field lines and they go into Saturn at different latitudes on the planet in something we call ring rain.

Because we can see in these latitude bands, there's water. And that water is coming from Saturn's rings. Wow. And the first thing I thought, it hadn't occurred to me before, but talking about those spiraling particles going in, it sounds almost as if you were looking at a cloud chamber on the end of some particle accelerator because of the same kinds of things happening, you know, reacting to a magnetic field. Right. It was just great to verify. And then in those final orbits, Cassini flew across those magnetic field lines and could directly measure the particles, how many of them and what they were made of.

So we got a close-up look to sample and taste the ring ring. As we see these things happening in the rings, and for example, that clumping of material around the midriffs of those little moons, is Saturn helping us to understand how our solar system and other solar systems may have been formed. Exactly right. By understanding how these particles stick together, how they interact in a disk, all of the things that go on give us clues to what that huge protoplanetary disk of material looked like and how clumps of material grew there that eventually became the planets. And we can apply that to our solar system and to exoplanet solar systems as well. So before we talk about the future, what have I missed?

What stands out? I think what stands out is just how much we still don't know and how long the list of questions still is. And there are many scientists happily working away, probably will continue to do so for decades to come, to look through that data set and learn more about the planet, the moons, and the rings themselves. And yet, do you ever stop now and then and think about how much we didn't know and now do know if you look back just 15 years when Cassini was arriving at Saturn. When Cassini first arrived at Saturn, we were literally standing on the shoulders of Voyager because we had the two Voyager flybys of the Saturn system and a Pioneer

flyby. And we thought we had lots of answers, But still, what was the source of the E-ring? Cassini found Enceladus with a liquid water ocean underneath its icy crust. We thought the rings were individual particles gently colliding, and now most of the ring material clumps together in very, very unusual and unique ways. The rings are young. Just so many things tightened, seeing the surface for the first time with the Huygens probe landing on the surface and finding methane lakes and seas and river channels and dunes of tiny particles that grow in the upper atmosphere. So many things that

kind of like, you know, maybe in a sense that with Wager we got closer to the cover of the book and Cassini is now opening and looking through the chapters and the pages of that book. And there's so much more to read. That's right. There's new books to write. In fact, many new books have come out from Cassini with Cassini data. There's a new book about Saturn, a new book about planetary rings, a new book about the icy moons and Enceladus. So we're,

in a sense, rewriting a lot of the history and a lot of what we thought we knew before Cassini. You've sort of touched on this, but what is currently on the frontier? What is the research that's underway now that will continue to build on this data. Those research in particular about Enceladus and how those jets work and come out of the surface, come out from Enceladus, to think about if we were going to land someday, you'd want to know as much about what is coming out and how close could you get and what kinds of instruments would you want to take for some kind of a lander mission on the moon Enceladus. Same thing for Titan. Looking in detail at those data, if you were going back to Titan,

say with an orbiter and maybe something to land on the surface, what questions and what things do you need to know about Titan, how the winds blow if you go down to the surface? You answer those questions as well. You must be very excited about this possibility of Dragonfly, that little autonomous drone going down to maybe explore the shores of Titan. That would be so, Dragonfly, if it's selected in NASA's New Frontiers program, would be such an exciting mission to really then be able to move to different locations on Titan

and take that one place that we know from the Huygens probe and start to really understand what's going on on Titan. And Dragonfly will be carrying the instruments that we've learned, as we've learned about Titan with Cassini, that will help answer additional questions. So hopefully a few months from now, we'll know if Dragonfly is the mission selected. Yeah, we're getting close. And of course, we don't play favorites at the Planetary Society. We wish that there was money for all of the missions that are in this current round of

competition because they all have tremendous value. But there certainly is something especially exciting about sending a flying machine to another world. Oh, absolutely. Just the picture of a quadcopter landing on Titan. It's really a cool mission. Well, what else is keeping you busy? I know that you're getting ready, helping to put together one of our favorite events around here, one that my colleague Emily Lakdawalla never misses.

Oh, yes. What's coming up is the DPS, or Division for Planetary Sciences, meeting. This year, it's a joint meeting with our European colleagues. It'll be held in Geneva, Switzerland, and it's going to be a huge meeting where planetary scientists from around the world come together, talk about their newest results, their newest science, and look forward to future missions as well. And as chair of the DPS, I'm helping plan and organize that meeting. And it's going to be a great meeting, Matt. Because now you have slightly more time than when you had a spacecraft

orbiting Saturn. Right, right. Now the Cassini, you know, that we're looking through the data, there's a bit more time to try and get the scientists together to talk about and encourage them to look at the data. Linda, it may not be quite as frequent as it was when Cassini was still sending back data, but we will continue, I hope, to have these conversations. Certainly by the time of DPS, because I bet there will be more research released at that time by your team when they meet with all their colleagues in Geneva. Right, man. I just want to add one more thing. Along with the science papers that came out, there's a special issue of the geophysical research letters, probably 40 or so additional papers on Cassini data. probably 40 or so additional papers on Cassini data. They've been online for a while, but now there's a special print issue that's available with additional papers,

a lot of them about this final year of the mission, in particular the grand finale. May the science continue to flow over the decades to come. I'm sure it will. Yes, I certainly hope so. Thank you, Linda. Thanks, Matt. That's Linda Spilker, project scientist for the Cassini-Huygens mission, telling us about the latest. And stay tuned because there is much more to come.

It is time for What's Up on Planetary Radio. Back with me is the chief scientist of the Planetary Society. That's Bruce Betts, Dr. Bruce Betts. Welcome. Thank you. Good to be here, Matt. How are you doing? I'm fine, and I only wish because we're having to record this before June 24th, because I'll be in Florida, because everything will be happening in Florida.

We don't know if LightSail has launched or not. We'll just have to keep our fingers crossed. I will still dare to talk about a light sail in this time period. I invite you to proceed and begin with the night sky. All right. In the night sky, you got Jupiter in the evening up in the east looking like a super bright star and Saturn coming up on Saturn opposition, opposite side of the Earth from the Sun. So it's rising just a little after sunset now. It'll pretty much be rising around the time of sunset when it reaches opposition in July.

It's total solar eclipse time. That's right. Total solar eclipse on July 2nd. And that will be visible from parts of the South Pacific and Chile and Argentina. At least totality, much of South America will see a partial solar eclipse. Yeah, I know our recent guest, Jay Pasikoff, he's going to be there in Chile waiting for, I don't know, something like his 40th total eclipse. Jeez, Amazing. This week in space history,

1908, Tunguska impact. As much forest from that asteroid impact airburst as 50% larger than the city of Los Angeles. It was pretty big. A lot of timber. Quite the reminder of,

hey, we need to do something about planetary defense, asteroid defense. Hey, by the way, I've got an asteroid defense class online. You can find it at courses.planetary.org. It'll only take you about an hour and you'll be a super asteroid defense smart. And it's free, right? It's free. All right, can we move on to random space fact? So LightSail 2, when you're building a spacecraft and you really want to think about it working, it's good to plan for contingencies. So we've actually built into LightSail 2, which LightSail 1 did not have,

a number of software timers that check things and figure out if processes need to be restarted or even the spacecraft rebooted. But we also have a hardware timer. So built into the hardware, there is a timer that a little more than 12 days into the mission, no matter what's happened or happening, it will reboot the spacecraft because, you know, rebooting your computer tends to fix stuff. Yeah, I keep telling my wife that. Maybe you need to build in a timer to just automatically reboot. That's a good idea. We keep saying that LightSail is the size of a loaf of bread.

Does it make toast? Yes, it does. But no one can eat it. In space, no one can eat your toast. That'd be a great tagline for a movie. I'm scared to think what that movie might be about. It would be scary. Yeah. We move on to the trivia contest, and we were playing Where in the Solar System? So Where in the Solar System is a feature named Dogana. How'd we do, Matt?

I know you're going to stick with that canine pronunciation of this, but I do think based on the responses we got, it's probably Dogana because it seems to be based on someplace in Italy. We'll get to that. Alex Schumann, he says it's a crater on Mars. That is correct. 41 kilometer crater on Mars. Congratulations, Alex. That is correct. 41 kilometer crater on Mars. Congratulations, Alex. First time winner. He listens to us on WMFE Orlando, not far from where LightSail will begin its historic mission, or maybe already has begun. a Planetary Society Kick Asteroid Rubber Asteroid, a 200-point itelescope.net astronomy account,

and a terrific book for young people, The Space Race by Sarah Cruddas, a beautifully illustrated book for young people about human space exploration and more. It's really delightful. It's full of great illustrations. So congratulations, Alex. Can I read you a few more? Oh, please do. This is from our friend Claude Plymate at the Big Bear Solar Observatory here in Southern California.

Dogana is a beautiful Martian crater, perfectly situated just north of the Valles Marineris, one of the wonders of the solar system. With superb views towards the outflow channels. This property is located at a temperate 10 degrees south, giving it some of the best weather on the planet, as well as plenty of solar exposure for your photovoltaic farm. Dogana is a perfect place for year-round living. The 41.2-kilometer diameter crater has plenty of room for your growing colony. Come for the views,

stay for the weather. I'm sold. The problem is, well, it's not there anymore, but as Laura Dodd and a few other people pointed out, it apparently used to have a lake. At least that's what a lot of researchers think, a paleo lake, which is a nice way to put it, I guess. Our poet laureate, I'm going to forego his poem this time because he provided such great information about this crater and its namesake on Earth. Southern hemisphere of Mars on Earth, this location would be on the eastern coast of Brazil. It is named for the largest town in San Marino, that little tiny nation that's totally surrounded by Italy. How small is it? Of interest, the entire country of San Marino would fit inside the crater 27 times with room to spare.

Great random space fact within the trivia. Indeed. I got one more, and this will be our poem for the week. David Dufet in Charlestown, West Virginia sent us this. On Mars, they might ask if you wanna go sightseeing at Crater Dogana, where a lake used to be, but today you won't see any water, nor flora, nor fauna. Nice work, David. Thank you very much. Got another one for us? I do. There is a mini DVD on LightSail 2 that contains the names of all of our Planetary Society members, Kickstarter backers, and people who signed up to send their names or selfies to space. On LightSail 2, what does the label of the mini-DVD say?

What are the words on the label of the mini-DVD? Go to planetary.org slash radio contest. You have until the 3rd of July, the day before Independence Day here in the U.S., July 3rd at 8 a.m. Pacific time to get us the answer this time. Somebody is going to win, I promise, a 200-point itelescope.net account, that worldwide network of telescopes anybody can use, if you have an account, to look at stuff all over the universe. A Planetary Society kick asteroid,

rubber asteroid, had trouble getting my engine started. And let's see, how about another book? Apollo, the graphic novel, which is, it's very cool. I have read it all. I have it here. And that's the copy that we'll make available. It actually does a fantastic graphic visual job of documenting not just the mission of Apollo 11, but to a degree, the lives of the three astronauts. And interestingly enough, one of the guys responsible, one of the three authors of this

graphic novel is named Mike Collins. Not that Mike Collins, but definitely Mike Collins, Michael Collins. We are ready to finish it off. All right, everybody, go out there, look up in the night sky, and think about where you'd buy property on Mars. Thank you, and good night. Dogona. I want the top of Mount Olympus.

You know why? Because that's where, according to Kim Stanley Robinson, they're going to put the bottom of the space elevator. So that property is going to be worth a lot. Oh, yeah. That's Bruce Betts, the chief scientist of the Planetary Society. He joins us every week here for What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California

and is made possible by our anxious yet thrilled members. Would somebody tell me if the launch went okay? Mary Liz Bender is our associate producer. Josh Doyle composed our theme, which was arranged and performed by Peter Schlosser. I'm Matt Kaplan, Ad Astra, and go light sail!